Touch panels are used for input and output interfaces of information apparatuses, e.g., Point of Sale (POS) systems, mobile devices, automatic teller machines (ATMs), cashers, kiosks, and interactive multimedia stations. Touch panels are typically categorized as pressure-sensitive touch panels, resistance type touch panels, surface sound wave type touch panels, capacitance touch panels, and infrared touch panels.
For optical touch panels such as infrared touch panels, a plurality of infrared transmitting devices and a plurality of infrared receiving devices are mounted on the printed circuit board thereof. The shape of the printed circuit board is typically rectangular, and the inner area of the printed circuit board is removed. Along one pair of opposite strips of the printed circuit board, the infrared transmitting devices and the infrared receiving devices are mounted and aligned to each other, and along the other pair of opposite strips of the printed circuit board, the infrared transmitting devices and the infrared receiving devices are mounted and aligned with each other. The aligned infrared transmitting devices and infrared receiving devices define a matrix of intersecting light beams that coincide with the graphical icons and the computer-generated graphics at the infrared touch panel. When the intersecting beams are disrupted by an object (e.g., the finger of a user), the position at which the disruption occurs may be precisely calculated.
Currently, optical touch panels mainly use liquid crystal displays (LCD) or the like, and they are illuminated by a back light source to increase the visibility of the display and enhance contrast thereof. Some optical touch panels have fixed brightness levels from their back light sources. When there is substantially consistent ambient light during operation of the display, the fixed brightness level may be suitable. However, in many situations in which devices use optical touch panels, a fixed brightness level may not be suitable. For example, energy may be wasted if devices such as POS systems, ATMs, kiosks, etc. are turned on at a fixed brightness level for a long period of time. In addition, some shops with alternate business hours may have lighting needs that change frequently, and thus energy may be wasted if the devices are turned on at a fixed brightness level for a long period of time. Moreover, energy may be wasted if the devices are turned on during non-business hours. Furthermore, leaving optical touch panels turned on unnecessarily will also shorten the life thereof, especially if the brightness level is high.
In addition, when the brightness level of the back light source is set to a specific value, the display brightness may be considered proper under normal lighting. However, there may be different ambient light levels in different environments where a user views the screen, and additionally there may be different ambient light levels during different periods of time when a user views the screen. In ambient light of low intensity, a user may prefer lower brightness levels for the display, because most can view the screen adequately at a relatively low brightness level. Conversely, in ambient light of high intensity, a user may prefer high brightness levels for the display. Thus, it is important to consider ambient light levels and to adjust display brightness level accordingly. Taking a POS system for example, in different locations (such as the extremes of a high-latitude location and a low-latitude location and in-between locations) or during different periods of time (such as the extremes of night and day and in-between periods), a fixed brightness level is not a good solution.
A solution could entail permitting a user to manually adjust the brightness level of the optical touch panel. However, such solution is usually considered troublesome, and a user tends to set the brightness to the maximum value, which may shorten the lifespan of the optical touch panel.
A further solution could entail adding an additional light sensor. However, such solution may increase manufacturing cost. In addition, the light sensor used in such solution (e.g., a CDS sensor) may have relatively unacceptable errors. Furthermore, the additional light sensor needed for such solution must be mounted on the optical touch panel, thus increasing assembly overhead.